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The last couple months I’ve been playing a lot of Half-Life multiplayer. HL is 12 years old, but still has a strong player base. Mainly because it’s fun, the graphics run great on almost any machine, and… there’s a strong player base.

Anyways, I’m a medium-skilled player– no longer a n00b, but only successful in certain circumstances. My aim is pretty terrible, and I’m not very good yet at defenses. But I’m smart, and on certain maps that’s all it takes.

Sunday mid-morning, there wasn’t much going on on my usual servers, but I ended up on a busy server with roughly 20 other people playing (I usually play against 5-6 people), and we ended up on a level with almost no cover, basically just a big open room with some ledges and things around the sides. On this kind of level, with this many people, there’s no chance of surviving more than a couple dozen seconds before somebody hits you with something that will kill you. That basically means rockets or the tau (sort of a ray-gun that a good direct hit will kill you immediately). My aim is pretty bad, so I tried the rockets, to minimum success. I actually managed to get one of the better players with the crowbar, mainly because he wasn’t looking for it.

So then I realize that this server is basically an “all-weapons” server– they give you max ammo and all weapons to start. So I have 10 grenades from the machine gun. These can go pretty far, and explode on impact. So I just start running around lobbing grenades at anything that moves, and focusing on not blowing myself up. IT WORKS, amazingly. Everyone else is running around with the tau or rockets and making kills here and there. I’m making 2-3 kills before I get killed, and then right back into. Most turns I managed to get all 10 grenades out before anybody hit me with anything.

So the map/level ends after 30 minutes, or when anyone gets to 60 kills. I got to 60 kills in like 15 minutes, the next-best score was around 40.

What’s the lesson here? If you find yourself out of your element, take a moment to look around and see if there’s a strategy that nobody else is trying that might work better. Give it a go, if it works, keep it up. If it doesn’t work, change until it does.

Here’s a screen cap showing the plane passing well infront of the GG bridge:

Now, it looks like it’s really close, but this video is being shot from Fisherman’s Wharf (lining up the hills behind the bridge and striking a line). At this point the north tower of the bridge is 4 miles away.

So, now we know our distance to the bridge: 21120 feet, the tower above the deck is 500 feet tall and takes up 3/4 of the frame. At the bridge’s distance, we’re seeing about 675 feet of height. That means we have an equivalent 750mm lens on the camera. The vertical FOV (the only one we can calculate with this data is 1.8 degrees). The total image (the screen cap above) is 378 pixels tall, for about 17.1 arc seconds per pixel.

Now comes the fun part — how far away is the airplane? We can pretty accurately measure the height of the fuselage, in the bulge. This comes out to 28 pixels. That’s 25′-10″ tall in real life. 28 pixels = 0.133 degrees. That’s 13.5% of the height of the image. Were that 747 in the same plane as the bridge, it would be 91 feet tall.

I solved it geometrically, rather than breaking out the trig. Drafting the triangle with 0.133 degrees for the near side, and a height of 25′-10″, we get a 11,128′ range, or about 2 miles — halfway to the bridge.

So — in short: the plane was nowhere near the bridge, it was about halfway between Alcatraz and the Bridge, and was never in danger of striking it. This illusion wouldn’t even have looked close were you standing at the Marina Green, as the plane would have been cornering almost right infront of you.

User says they shot it with a Canon Powershot SX20IX, which has a maximum focal length equivalent of 560mm (100mm on a 1/2.3″ sensor). So that’s 2.5 degrees vertical over 675 feet. We get 15460 feet, which is only about 3 miles, meaning they were closer than Fisherman’s wharf. 13.5% of 2.5 degrees is 0.3375 degrees, meaning the airplane was 4384 feet away, or 0.8 miles. Still, the plane was at least 2 miles from the bridge.

I spent the last weekend working on an IMU-based control system for an RC airplane. I came across several bits of code that could be useful to the masses (at least, the programming masses).Continue reading →